1. Field of the Invention
The present invention relates to down pressure controls for grain drill furrow openers.
2. Prior Art
In the prior art, most grain drills had down pressure for the furrow openers controlled by a compression spring that was mounted on a telescoping rod and which would exert a down pressure increasing directly proportional to the spring movement. The depth of the openers generally was controlled proportional to the amount of down pressure on the individual furrow openers.
One of the problems in the down pressure controls was that in hard ground, for example where minimum tillage practices are being followed, by the time the springs had been compressed enough to exert a sufficient down pressure on the furrow openers, the springs were almost bottomed out, and then if the furrow openers struck a rock or other obstruction something would have to give and usually would break. Further, even if the depth control springs had some range of movement, the normal up and down movement of the furrow openers was sufficient to cause high spring load changes, which would overload and damage the individual parts.
General examples of down pressure controls utilizing spring force for keeping the furrow openers in the ground are shown in U.S. Pat. Nos. 2,155,443; 3,005,426; 3,228,363 and 2,738,969.